Yes, the blue card is for DVC members. From what I understand, you can only be a DVC member if you purchased your time share directly from Disney. If you purchased your time share via resale or are renting points then you are not eligible for the DVC member perks (i.e. free parking, member events, discount's, etc).
I'm sure there will be some that say it shouldn't matter since I am staying on points, etc. But, people have to remember/know that if you purchased directly with Disney, then you paid FULL price for the points that were purchased. From what I've seen, you pay a lot less when purchasing a Disney time share via resale or renting points for a vacation. So for me I can see the logic on why you have to verify being a DVC member. Without opening up a spreadsheet, I'm pretty sure that since DVC members paid full price for their points we're definitely over "paying" for overnight parking